Abu Ishaq said: I heard Sayyiduna Ibn Umar (may Allah be pleased with them both) saying between Safa and Marwah: "Rabbi ighfir warham, wa anta al-a'azzu al-akram" (My Lord! Forgive me and have mercy, and You are the Most Mighty, the Most Generous).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9352